Self-supporting shadow mask for colored tv picture tubes



N. B. MEARS Nov. 18, 1969 SELF-SUPPORTING sHADow MASK FOR COLORED TvPICTURE TUBES Filed June 11, 1968 INVENTOR NORMAN B. MEA/R9 AT RNEYSUnitedStates Patent O 3,479,546 SELF-SUPPORTING SHADOW MASK FOR COLOREDTV PICTURE TUBES Norman B. Mears, St. Paul, Minn., assignor to Buckbee-Mears Company, St. Paul, Minn., a corporation of Minnesota Filed June11, 1968, Ser. No. 736,192 Int. Cl. H01j 29/46 U.S. Cl. 313-85 8 ClaimsABSTRACT F THE DISCLOSURE A shadow mask for colored TV picture tubes isconstructed with the conventional translucent area formed by a multiudeof tiny apertures in a slightly bowed-out metal sheet through which theelectron beams pass from the electron guns at the rear of the tube tothe viewing face at the front of the tube. Integrally `formed with thetranslucent area is a circumambient imperforate rim which has astrengthening bead to make it quite rigid. An inward flaring flangeextends around the edge of the rim to form a haze shield. The mask ismounted to the glass bulb of the picture tube by metal spring-likemembers which are attached at one end to the outside of the rim and atthe other end are secured to the envelope of the tube.

BACKGROUND OF THE INVENTION Field of the invention This invention isdirected toward use specically in the construction of color TV picturetubes containing aperture or shadow masks.

Description of the prior art In the past the aperture masks have beenmade out of flat sheets of thin metal such as stainless steel, with thetranslucent area surrounded by an imperforate marginal area. The maskwas then bowed or made somewhat concave to conform to the contour of thefront face of the picture tube. It is then mounted on a fairly massivemounting ring which in turn is fastened to the inside of the picturetube bulb by suitable attachments. Not only are masks made in thismanner somewhat more costly, but the mounting hardware adds considerableweight and cost. Because of its mass, the mounting hardware usuallyproduces some fairly substantial temperature gradients over the breadthof the mask during normal use. This results in some warping or twistingof the mask within the tube and adversely affects registration of thedot-like apertures to the phosphor dots and the definition of thepicture viewed on the face of the tube, at least until the entire maskreaches a uniform constant temperature. Furthermore the mounting ringtechnique is time consuming since the mask must be assembled to the ringbefore being mounted within the tube envelope. A recent innovation is aself-supporting mask which eliminates the massive mounting ring and thehardware associated therewith. This innovation is described in U.S.Patent 3,376,45'1.

SUMMARY The present invention, sometimes referred to as a uniframe mask,is somewhat of a variation of the selfsupporting mask described in theaforementioned patent. It contains the conventional bowed-out or concavetranslucent area but the circumambient 90 rim is strengthened with acontinuous bead or rib and the metal sheet is terminated with an inwardflaring ange around the edge of the rib, all to provide self supportingstrengthening features to eliminate the need for additional supportingstructure. The uniframe mask is mounted to the inside of the picturetube bulb by elongated, spring-like members attached at one end to therim and at the other end to the inside of the picture tube bulb. Notonly is the mask then easily removable and reinsertable at the exactsame location, but this type of construction is of considerable lessweight. Even more important is that the entire mask area warms up at thesame rate so that there is virtually no temperature differential acrossthe mask, at least not enough to cause any twisting or warping whichwould impair the quality of the picture being projected on the viewingface. Furthermore, the basic cost of the mask is reduced as well as thecost of assembly of the picture tube, at least that part allocated toassembly and mounting of the aperture or shadow mask.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is the rear view of a shadowmask for a colored TV picture tube constructed according to theteachings of this invention;

FIG. 2 is a front View of the same shadow mask;

FIG. 3 is a top view of the same shadow mask;

FIG. 4 is a side view of the same shadow mask;

FIG. 5 is a sectional view along viewing line 5 5; and

FIG. 6` illustrates in greater detail some of the features of theconstruction of the spring mounts for the shadow mask.

DESCRIPTION OF THE PREFERRED EMBODIMENT The conventional shadow mask oraperture mask for a colored TV picture tube contains a transducent area10 formed by a myriad of tiny dot-like apertures which are usuallyetched through a sheet of metal such as stainless steel. The aperturemask may be circular or rectangular depending on the tube type. Theelectron beams pass through the openings in the translucent area as theyare ejected from electron guns located at the rear of the tube andtravel towards the phosphor particles on the inside of the viewing faceof the tube. As seen most clearly in FIGS. 3 and 4, the mask,principally the translucent area, is bowed or concave to generallyfollow the contour of the inside face of the picture tube. The mostpopular way of mounting the shadow mask within the picture tube has beenwith a heavy mounting ring and associated hardware with the mask beingattached to the ring along the imperforate marginal area 11. In thisinvention this mounting ring, and its associated disadvantages, iseliminated.

The uniframe aperture mask of the present invention contains theconventional translucent area 10 surrounded by the marginal imperforatearea 11. Extending rearward at about from a planar projection of thetranslucent area is an integral continuation of the imperforate sectionforming a deep drawn rim 12 completely around the aperture mask. The rim12 is formed with an elongated continuous inner bead or outer groove 13which serves to strengthen the rim area 12. The rim 12 terminates withan integral continuation of the imperforate section aring inward to forma flange 14 extending around the entire rear edge of the rim. The latterprovides what is commonly referred to as a haze shield which eliminatesor minimizes the hazy eifect that might otherwise be present because ofthe dispersal of the electron beam pattern. The haze shield area 14 isterminated by a tiny upturned lip 15 which denes the 'outer dimensionsof the opening through which the electron beams travel from the electronguns, not shown, through the translucent area 10. An aperture maskconstructed in this manner has a degree of rigidity and a substantialdegree of resiliency so during normal handling prior to beingpermanently installed inside the envelope of the colored TV picturetube, even though it may be twisted somewhat or otherwise subjected tovarious forces, it returns to its original shape when the force isremoved. Therefore it can be handled with a great deal less care thanhas been the case with the shallow drawn aperture mask of the pastbefore it was mounted on and supported by the heavy -mounting ring.Attached to the outside of rim 12, preferably at three points asillustrated in the drawings, are mounts 16 for attaching the selfsupporting shadow mask to the envelope of the picture tube. Preferablythe mounts 16 are attached to the rim by spot welding the at plateportion 16a to the rim 12, but, of course, other methods of attachmentcan be utilized. The mounts 16 are made out of a strip of metal, such as301 stainless steel. In the center area of the strip a section ispunched out to form tongue member 17 which protrudes angularly outwardfrom 16a and remains joined thereto at one end 18. At its other end thetongue member 17 is bent to form tab 19 for resting against the innersurface of the picture tube envelope. A hole 20 is pierced through thetab area 19 for engaging mounting pins or studs suitably located andjutting inward from the picture tube envelope. The tongues 17 on themounts 16 are characterized by a degree of resiliency which, when themask assembly is temporarily mounted in the tube envelope, removed andthen later reinstalled, will make the translucent area of the shadowmask return to its original location with respect to the front face ofthe picture tube which is necessary to maintain register between theminiature apertures in the translucent area and their respectivelyassociated phosphor dots on the inner front face of the tube.

Although in the embodiment described herein only a single strengtheningbead 13 is shown in rim 12, it is contemplated that the mask can beformed with a number of similar strengthening beads or ribs in the rimto provide the desired rigidity and resiliency. It is also contemplatedthat if necessary, strengthening ribs or beads can be formed in theiiange 14 which serves as the haze shield. The additional strengtheningribs may take the form of continuous elongated beads or may bediscontinuous, such as parallel elongated ribs in the upper and lowerportions of liange 14 or in the left and right side portions.

Although not shown in the drawings, ordinarily when the aperture mask orshadow mask is inserted in the picture tube envelope, it is providedwith a lbeam shield which is an annular ange which extends outwardaround the outer rear edge of the mask, usually from the area whereflange 14 meets the rear edge of the rim 12. The beam shield extendsoutward to the glass envelope and serves to cut down spuriousreflections which might otherwise interfere with the view of the pictureat the front of the tube. It is contemplated that a beam shield may beincorporated in the present invention as an integral part of the mask bybeing a continuation of the imperforate section of the rnetal sheetwhere lip is shown in the drawing. In other words, a beam shield may beformed by a ange flaring outward at a sharp angle to the edge of flange14 so that its outer edge rests against the inside surface of the tubeenvelope. A flange of this nature not only will perform the necessaryfunction of a beam shield but also provides additional strengthening tothe overall construction of the uniframe mask- It is also contemplatedthat a funnel-shaped magnetic shield may be made a part of the uniframemask assembly by being attached at the rear of the mask in a mannersimilar to that illustrated and described in U.S. Patent 3,376,451.

There will now be briefly described a method by which a uniframeaperture or shadow mask has been constructed according to the teachingsof this invention. Initially the translucent area 10 must be formed in asheet of metal of suitable size. Typically, stainless steel sheet, inthe range of .01 inch thick, may be utilized and the size of the sheetand the translucent area is dictated by the size and shape of thepicture tube in which the mask will `be used. Typically, the translucentarea can be formed in the manner described briefly in U.S. Patent No.3,313,225 of Norman B. Mears and other patents referred to therein.Briefly, this involves the steps of coating both sides of a fiat sheetof metal with a suitable light-sensitive enamel and after drying,projecting a pattern of a multitude of miniature dots, using a suitablelight source, on both sides of the coated metal sheet in register sothat the enamel coating hardens only where struck by light. Theunhardened enamel is then removed and the coated metal is immersed orsprayed or otherwise subjected to a suitable chemical etchant whichremoves the metal from the unprotected areas to form the desired patternof miniature holes which comprises the translucent area of the aperturemask. This process of photochemical etching is commonplace in thephotoengraving art and other fields today.

Once the translucent area is formed in the flat Sheet of metal, asuitably sized blank is cut roughly to size out of the metal sheet. Thisincludes the translucent area. The roughly cut blank is then annealed ata temperature in the range of 1,600 F. for a suitable period of time.Following this, after an adequate cooling time, the metal blank isroller-leveled once on each side. This is accomplished by applyingpressure on the sheet with rollers. This is done to relieve some of theinternal stresses and strains which might have developed in the metalsheet. After roller leveling, the blank is cut to the exact size andinserted into a die block having a male and female portion for forming.If a rectangular mask, such as illustrated in the drawing, is to beformed, notches are cut in the four corner areas. The blank is then heldin suitable fashion in the die block and the rim is drawn down to thedesired depth. Because of the nature of the material, the depth of thedraw, the criticality of aperture locations and other factors, it may bepreferable to draw the rim to prescribed depth in a step-by-stepfashion. For example, an initial draw may be to :A3 inch then to inch,then to M; inch and finally to a rim of 11/2 inches. Suiable dies forforming the uniframe mask can be designed by those skilled in the artand various procedural steps are readily determinable by those skilledin the art of die forming.

After the rim 12 has been formed, the flange or haze shield 14 is formedby flaring the remainder of the imperforate sheet of metal inward alongthe edges of the rim. Preferably this should be done by first flaringthe long sides of the rim, then the shorter sides and next pressing thecorner areas inward. The mask is then clamped in a suitable fixture andthe corners and gussets are spot welded. Next, while the mask is held inanother suitable fixture, mounts 16 are spot welded at suitablelocations to the outside of rim 12. Lastly, the strengthening rib or rib13 is formed in the rim 12 while the mask is held securely in a fixture.

It should be understood, of course, that the foregoing brief descriptionof the process for forming a uniframe mask is only intended to beillustrative and not limitive since it is contemplated that the formingoperation can be accomplished in a variety of manners.

I claim:

1. An improved self-supporting shadow mask for a colored TV picture tubemade from a thin metallic sheet, comprising: a concave translucent areadefined by a myriad of miniature dot-like apertures through the metallicsheet; an imperforate section of said metallic sheet forming a rimcircumambient to said translucent area extending rearward therefrom asubstantially a angle to the planar projection of the translucent area;a continuous elongated strengthening bead formed on said rim; a furtherimperforate section of said metallic sheet forming a flange flaringinward from the rear edge of said rim; and means located on the outsideof said rim for mounting the mask to the picture tube bulb.

2. The invention as described in claim 1 wherein said means for mountingthe mask is attached directly to said rim.

3. The invention as described in claim 2 wherein said mounting meansincludes an elongated resilient metallic tongue extending angularlyoutward from said rim being joined at one end only to said rim and beingcoupled to the tube bulb near its other end.

4. The invention as described in claim 2 wherein said mounting meanscomprises: a relatively thin strap of stainless steel aixed to theoutside of said rim; a resilient tongue member formed out of a centralportion of said strap, said tongue member extending angularly outwardfrom said strap and having a tab portion at its free end bent to restagainst the inside of the tube bulb, said tab portion containing anopening for engaging a mounting pin extending inwardly from said bulb.

5. The invention as described in claim 3 further including elongatedstrengthening beads on -said flange.

6. For a color TV shadow mask made out of a metal sheet having a curvedtranslucent face area surrounded by an imperforate rearward directed rimsection with a continuous elongated strengthening bead on said rim,means for attaching the mask to the tube, comprising: mounting meansattached to said rim on at least three sides of the mask, each of saidmounting means having an elongated resilient metal tongue memberextending angularly outward from said rim being attached to the rim atone end and being coupled to the tube bulb at its other end.

7. The invention as set forth in claim 6 wherein each of said mountingmeans comprises: a strap of metal rigidly secured to the outside of saidrim; a resilient tongue member formed out of a portion of said strap andextending angularly outward from the strap, said tongue member having atab portion at its free end bent to parallel the inside of the tube bulband containing an opening adapted to engage a mounting pin in said bulb.

8. The invention as set forth in claim 7 wherein said strap bridges thebead on said rim.

References Cited UNITED STATES PATENTS 2,855,529 10/1958 Morrell 313-85X3,368,098 2/1968 Demmy 313-85 I AMES W. LAWRENCE, Primary Examiner V.LAFRANCHI, Assistant Examiner

